The present invention relates to a battery monitoring system and a semiconductor device. More specifically, the present invention relates to a battery monitoring system and a semiconductor device suitable for monitoring a plurality of batteries connected in series.
In general, a high capacity and high output battery has been used for driving a motor of a hybrid automobile or an electric automobile, and the like. The high capacity and high output battery may be formed of a battery unit (for example, a lithium-ion battery unit), in which a plurality of batteries (battery cells) is connected in series. A conventional battery monitoring system has been developed for monitoring a voltage of the batteries of the battery unit.
As the conventional battery monitoring system, there has been known a configuration thereof, in which a highest potential (a potential at the highest level) of the batteries connected in series is supplied to a semiconductor device as a drive power source of an internal circuit of the semiconductor device having a battery monitoring circuit (a battery measurement circuit).
Patent Reference No. 1 has disclosed the conventional battery monitoring system. The conventional battery monitoring system disclosed in Patent Reference No. 1 is provided with a battery cell controller, in which a voltage of the highest potential of the battery cells supplied through a VCC terminal is used for driving the internal circuit thereof. In the battery cell controller of the conventional battery monitoring system disclosed in Patent Reference No. 1, a main constant voltage power source (a regulator) is provided for converting the voltage of the highest potential of the battery cells to a voltage for driving the internal circuit and the like.
Patent Reference No. 1: Japanese Patent Publication No. 2010-16928
Patent Reference No. 2 has disclosed a conventional technology, in which an electro-static charge protection circuit is provided in a semiconductor device for preventing damage on the internal circuit of the semiconductor device caused by electro-static charge. In the conventional technology disclosed in Patent Reference No. 2, the semiconductor device includes an ESD (Electro-Static Discharge) protection diode for discharging a high voltage noise due to the electro-static charge to a power source terminal.
Patent Reference No. 2: Japanese Patent Publication No. 2011-96897
FIG. 5 is a schematic diagram showing a configuration of a conventional battery monitoring system 100 having the electro-static charge protection circuit. In the conventional battery monitoring system 100 shown in FIG. 5, the electro-static charge protection circuit disclosed in Patent Reference No. 2 is disposed in the semiconductor device of the conventional battery monitoring system (refer to Patent Reference No. 1), so that it is possible to prevent damage caused by the electro-static charge on the internal circuit of the semiconductor device of the conventional battery monitoring system.
As shown in FIG. 5, the conventional battery monitoring system 100 includes a battery cell unit 112, in which a plurality of battery cells C (C1 to Cn) is connected in series, and a semiconductor device 120 connected to the battery cell unit 112 through low pass filters LPF (LPF1 to LPFn, and LPFvcc). Further, the semiconductor device 120 includes a battery cell voltage measurement circuit 122. The battery cell voltage measurement circuit 122 includes a regulator for converting a power source voltage Vcc supplied to the battery cell voltage measurement circuit 112 to a drive voltage, and an electrical current driven type circuit such as an internal processing circuit to be driven with the drive voltage converted with the regulator.
In the conventional battery monitoring system 100 as shown in FIG. 5, the power source terminal Vcc of the semiconductor device 120 is connected to a battery cell input signal line Ln through the low pass filter LPFvcc, and the battery cell input signal line Ln is connected to a high potential side of the battery cell Cn of the battery cell unit 112 on the highest potential level. Accordingly, the power source voltage Vcc is supplied to the semiconductor device 120 (the power source terminal Vcc) through the battery cell input signal line Ln.
In the conventional battery monitoring system 100, the power source terminal Vss of the semiconductor device 120 is connected to a battery cell input signal line L0, and the battery cell input signal line L0 is connected to a low potential side of the battery cell C1 of the battery cell unit 112 at the lowest potential level. Further, the power source line Vcc connected to the power source terminal Vcc and the power source line Vss connected to the power source terminal Vss are connected to an inter-power source ESD protection circuit 124.
In the conventional battery monitoring system 100, cell input terminals V (V1 to Vn) of the semiconductor device 120 are connected to cell input signal lines L (L1 to Ln) that are connected to the high potential side of each of the battery cells C1 to Cn through the low pass filters LPF (LPF1 to LPFn), respectively. Further, the cell input terminals V (V1 to Vn) of the battery cells C1 to Cn are connected to the battery cell voltage measurement circuit 122 through the cell input signal lines L (L1 to Ln) that are connected to ESD protection diodes ESD (ESD1 to ESDn), respectively.
In the conventional battery monitoring system 100, the low pass filters LPF (LPF1 to LPFn) have a function of removing an external turbulent noise contained in the cell voltage input thereto. Further, the low pass filter LPFvcc has a function of preventing a potential from generating between the power source terminal Vcc and the cell input terminals V (V1 to Vn) due to a phase difference upon passing through the low pass filters LPF (LPF1 to LPFn), and has a characteristic similar to that of the low pass filters LPF (LPF1 to LPFn).
In the conventional battery monitoring system 100, the ESD protection diodes ESD (ESD1 to ESDn) have a function of discharging a high voltage noise due to the electro-static charge and the like to the power source terminal Vcc or the power source terminal Vss (the inter-power source ESD protection circuit 124).
In the conventional battery monitoring system 100 having the configuration described above, during the normal operation (that is, when the voltage of the battery cells C is measured, and the like), an electrical current Icc flows into the power source line Vcc (the battery cell voltage measurement circuit 122, the regulator, and the like) through the power source terminal Vcc. More specifically, the power source line Vcc is connected to the circuit of the electric current driven type such as the battery cell voltage measurement circuit 122, the regulator, and the like. Accordingly, the electrical current Icc (the power consumption current Icc) flows into the power source line Vcc for driving the circuit of the electric current driven type.
When the electrical current Icc flows into the power source line Vcc, a voltage drop occurs due to a resistor Rvcc of the low pass filter LPFVcc. If the voltage drop exceeds a diode forward direction voltage of the ESD protection diode ESDn, even during the normal operation, an electrical current may flow into the power source terminal Vcc (the inter-power source ESD protection circuit 124) from the battery cell Cn through the ESD protection diode ESDn. When such an electrical current flows into the power source terminal Vcc, the voltage of the cell input terminals V (V1 to Vn) decreases. As a result, the voltage drop at the cell input terminals V (V1 to Vn) causes a measurement error of the battery voltage of the battery cells C (C1 to Cn) in the battery cell voltage measurement circuit 122.
In order to prevent the voltage drop caused by the resistor Rvcc of the low pass filter LPFVcc, the conventional battery monitoring system 100 may be configured such that the cell input signal line Ln is directly connected to the power source terminal Vcc without passing through the low pass filter LPFvcc. When the cell input signal line Ln is directly connected to the power source terminal Vcc, it is possible to prevent the voltage drop caused by the resistor Rvcc of the low pass filter LPFVcc. In this case, however, the following problems may occur.
As described above, in the conventional battery monitoring system 100, the battery cell unit 112 is configured to supply the voltage to the device (for example, a motor and the like) to drive the device. When a noise is generated in the device due to driving of the device (for example, a startup power and the like), the voltage of the battery cell unit 112 as a whole may be fluctuated. When the cell input signal line Ln is directly connected to the power source terminal Vcc without passing through the low pass filter LPFvcc, the potential of the power source terminal Vcc may become lower than the potential of the cell input terminals V (V1 to Vn) due to an influence of the noise. When the potential of the power source terminal Vcc becomes lower than the potential of the cell input terminals V (V1 to Vn), the electrical current flows from the battery cells C (C1 to Cn) to the power source terminal Vcc (the inter-power source ESD protection circuit 124) through the ESD protection diodes ESD (ESD1 to ESDn).
As described above, in the conventional battery monitoring system 100, even in the normal operation, the electrical current may flow from the battery cells C (C1 to Cn) to the power source terminal Vcc (the inter-power source ESD protection circuit 124) through the ESD protection diodes ESD (ESD1 to ESDn).
In view of the problems described above, an object of the present invention is to provide a battery monitoring system capable and a semiconductor device of solving the problems of the conventional battery monitoring system. In the present invention, in the normal operation, it is possible to prevent an electrical current from flowing to a discharge circuit from a battery cell through an electro-static charge protection circuit.
Further objects and advantages of the invention will be apparent from the following description of the invention.